Hormones in felines can get out of wack just like in humans.
Visitors Ask Questions about Behavior that May be Related to Hormone Levels
Feline Hormone Levels May be High
We have two male cats that we got from the Humane Society. They are brothers. They were neutered before we got them home, even though they were over a year old. Now, they are about two years old. One of the male cats is humping his brother all the time! They have plenty of toys, scratching posts and seem to be pretty normal healthy cats. The brother that keeps getting mounted doesn't do much to stop it. This usually occurs at night, but does happen a lot during the day. It seems to be an obsession. The cat does not do this with stuffed animals or anything else. Just to his brother. Thanks for your help.~~Cris
Although I have heard other pet owners complain about this problem from time to time in neutered male cats, the fact that your cat is doing this so frequently is of some concern to me. There are many reasons why a cat might hump another, but probably the most common reasons are dominance issues and hormonal imbalances. Since this is a recent behavior, I would probably take him to the vet and ask for blood work on his hormone levels. In fact, it might be a good idea to have blood work done on both cats to make sure nothing unusual is going on with the other cat receiving all the attention.
Although the behavior is something you don't want your cat to engage in when you have company over, since it is not bothering the other cat at this time, I would ignore it until you get those test results back. And if company does come over, put the cats in a separate room.
Another thing you could try as a temporary measure is separating the two cats when you are not there to monitor them and at night so you can rest. When you are home and your cat begins to hump his brother, tell the cat no and distract him with a favorite toy. When he stops on his own, praise him enthusiastically and give him a treat. It is very hard to train cats unless you use positive reinforcement.
I hope this helps. Let us know what the vet says about his hormone levels.
Renal Failure and Increased Sexuality
We have two cats. The cats are brother and sister and are seventeen years old. Both were neutered/spayed as kittens. In the last six months, we have been infusing the male cat with Ringers Solution because of his diagnosis of chronic renal failure. In the last month or so, he has begun to demonstrate excessive humping activity with his sister, both day and night and is clearly sexually stimulated. Could this be a hormone imbalance due to the weekly infusion of 200 ml of the solution? No other medications or dietary changes have occurred.
Ringers Solution is generally given to help with electrolyte depletion but is also commonly given to cats with renal failure too. The only side effects are usually some pain and swelling at the site of injection and I couldn't find any documentation for an increase in sexuality in cats taking this solution.
More than likely, the male cat has some type of hormonal imbalance which is probably tied into the other issues he is experiencing as he ages. Hormonal imbalances can be common in elderly cats. I would have the vet test him for high hormone levels and see if this is the issue, which can be corrected with appropriate medication.
I hope this helps and please check back and let us know if this was the problem. Good luck!